1. Field of the Invention
The present invention relates generally to the field of disk drive manufacturing. In particular, embodiments of the present invention are drawn to robotic machines for picking and placing workpieces such as screws on selected features of a hard disk drive being manufactured.
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a slider with at least one transducer or read/write element for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to “load” the slider against the disk. When the disk or disks are spinning, sliders develop an air bearing relative to the spinning disks that results from a converging channel and from the viscosity of the air. Indeed, a rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. In this state, the slider is commonly said to be “flying”, although the sliders do not, in fact, fly or develop an aerodynamic force like lift (as air foils do due to the Bernoulli effect).
Advances in the hard disk drive industry have led to the incorporation of disk drives into a variety of hand held devices, such as music players, cameras and PDAs. The small size of such devices has led to a corresponding reduction in the form factor of high capacity hard disk drives. Conversely, the ability of manufacturers to introduce ever smaller drives has led to their incorporation in ever widening classes of electronic devices and to the development of entirely new classes of devices. Form factors have steadily shrunk from 5.25″, 3.5″, 2.5″, 1.8″ and now to 1 inch and smaller drives. As a result of such continuing miniaturization, many of the constituent components of the drives have become too small to be consistently, speedily and reliably handled by human hands. For example, screws that are used in such small form factor drives include so-called 1M screws, which have a diameter of just 1 mm and a head height of just 0.2 mm. These screws are difficult to pick up, couple to a screw driver and drive into a selected threaded hole in a disk drive. Often, such small screws are accidentally driven at an angle into the threaded hole, which may cross-thread the hole and damage the drive. Moreover, as the screws and corresponding holes are so small, manual over-torquing of the screws is also a problem. Even when such small screws are correctly aligned with their intended threaded hole and correctly driven therein, human operators are slow and cannot reliably repeat such precision movements for any extended length of time. Moreover, it has proven to be difficult to manually tighten and loosen these micro screws without breaking them. Thus, broken screws and particulate contaminants from cross-threading may contaminate the disk drives and/or cause operational failures. This decreases the production line's yield. Similar problems are encountered with other drive components, such as, for example, ramp load assemblies and head stack assemblies (HSAs).
Such problems have led to the development of screw driving machines. These machines are traditionally configured to drive screws into threaded holes to a constant and predetermined distance. This constant and predetermined distance is conventionally calculated from the pitch value and the number of turns of threads of each screw. However, while such a process has worked reasonably well for screws larger than M4 or 4-40 screws, the process's disadvantages reveal themselves when applied to smaller screws. For example, for Ml screws currently used in small form factor disk drives, such a process based upon the pitch value and the number of threads tends to lead to an unacceptably high number of high screws (screws that are not fully driven into their threaded holes), cross-threading and other damage to the screws and/or threaded holes, with consequent unwanted generation of particulate matter and decrease in yield. It has become apparent that improved methods, devices and systems for driving small screws into disk drives are needed.